Stent designs for use in peripheral vessels

ABSTRACT

Stent designs for use in peripheral vessels, such as the carotid arteries, are disclosed. The stents consist of a plurality of radially expandable cylindrical elements generally aligned on a common longitudinal stent axis and interconnected by one or more interconnecting members placed so that the stent is flexible in a longitudinal direction. The cylindrical elements are generally serpentine wave pattern transverse to the longitudinal axis between alternating valley portion and peak portions, the valley portion including alternating double-curved portions and U-shaped portions. The interconnecting members are attached to the double-curved portions to connect a cylindrical element to an adjacent cylindrical element and interconnecting members are attached to the U-shaped portions to connect the cylindrical element to the other adjacent cylindrical element. The designs include an eight crown and six crown stent which exhibit flexibility and sufficient radial strength to support the vessel.

[0001] This application is a continuation of Ser. No. 09/475,393 filedon Dec. 30, 1999, which is assigned to the same Assignee as the presentapplication.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to expandable endoprosthesisdevices, generally called stents, which are adapted to be implanted intoa patient's body lumen, such as a blood vessel, to maintain the patencythereof. Stents are particularly useful in the treatment and repair ofblood vessels after a stenosis has been compressed by percutaneoustransluminal coronary angioplasty (PTCA), percutaneous transluminalangioplasty (PTA), or removed by atherectomy or other means, to helpimprove the results of the procedure and reduce the possibility ofrestenosis.

[0003] Stents are generally cylindrically- shaped devices which functionto hold open and sometimes expand a segment of a blood vessel or otherarterial lumen, such as coronary artery. Stents are usually delivered ina compressed condition to the target site and then deployed at thatlocation into an expanded condition to support the vessel and helpmaintain it in an open position. They are particularly suitable for useto support and hold back a dissected arterial lining which can occludethe fluid passageway there through.

[0004] A variety of devices are known in the art for use as stents andhave included coiled wires in a variety of patterns that are expandedafter being placed intraluminally on a balloon catheter; helically woundcoiled springs manufactured from an expandable heat sensitive metal; andself-expanding stents inserted into a compressed state for deploymentinto a body lumen. One of the difficulties encountered in using priorart stents involve maintaining the radial rigidity needed to hold open abody lumen while at the same time maintaining the longitudinalflexibility of the stent to facilitate its delivery and accommodate theoften tortuous path of the body lumen.

[0005] Prior art stents typically fall into two general categories ofconstruction. The first type of stent is expandable upon application ofa controlled force, often through the inflation of the balloon portionof a dilatation catheter which, upon inflation of the balloon or otherexpansion means, expands the compressed stent to a larger diameter to beleft in place within the artery at the target site. The second type ofstent is a self-expanding stent formed from shape memory metals orsuper-elastic nickel-titanum (NiTi) alloys, which will automaticallyexpand from a compressed state when the stent is advanced out of thedistal end of the delivery catheter into the blood vessel. Such stentsmanufactured from expandable heat sensitive materials allow for phasetransformations of the material to occur, resulting in the expansion andcontraction of the stent.

[0006] Details of prior art expandable stents can be found in U.S. Pat.No. 3,868,956 (Alfidi et al.); U.S. Pat. No. 4,512,1338 (Balko et al.);U.S. Pat. No. 4,553,545 (Maas, et al.); U.S. Pat. No. 4,733,665(Palmaz); U.S. Pat. No. 4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882(Gianturco); U.S. Pat. No. 5,514,154 (Lau, et al.); U.S. Pat. No.5,421,955 (Lau et al.); U.S. Pat. No. 5,603,721 (Lau et al.); U.S. Pat.No. 4,655,772 (Wallstent); U.S. Pat. No. 4,739,762 (Palmaz); and U.S.Pat. No. 5,569,295 (Lam), which are hereby incorporated by reference.

[0007] Further details of prior art self-expanding stents can be foundin U.S. Pat. No. 4,580,568 (Gianturco); and U.S. Pat. No. 4,830,003(Wolff, et al.), which are hereby incorporated by reference.

[0008] Expandable stents are delivered to the target site by deliverysystems which often use balloon catheters as the means for deliveringand expanding the stent in the target area. One such stent deliverysystem is disclosed in U.S. Pat. No. 5,158,548 to Lau et al. Such astent delivery system has an expandable stent in a contracted conditionplaced on an expandable member, such as an inflatable balloon, disposedon the distal portion of an elongated catheter body. A guide wireextends through an inner lumen within the elongated catheter body andout its distal end. A tubular protective sheath is secured by its distalend to the portion of the guide wire which extends out of the distal endof the catheter body and fits over the stent mounted on the expandablemember on the distal end of the catheter body.

[0009] Some prior art stent delivery systems for implantingself-expanding stents include an inner lumen upon which the compressedor collapsed stent is mounted and an outer restraining sheath which isinitially placed over the compressed stent prior to deployment. When thestent is to be deployed in the body vessel, the outer sheath is moved inrelation to the inner lumen to “uncover” the compressed stent, allowingthe stent to move to its expanded condition into the target area.

[0010] In many procedures which utilize stents to maintain the patencyof the patient's body lumen, the size of the body lumen can be quitesmall which prevents the use of some commercial stents which haveprofiles which are entirely too large to reach the small vessel. Inparticular, often in PTCA procedures, the stenosis is located in thevery distal regions of the coronary arteries which often have smalldiameters. Many of these distal lesions are located deep within thetortuous vasculature of the patient which requires the stent to not onlyhave a small profile, but also high flexibility to be advanced intothese regions. As a result, the stent must be sufficiently flexiblealong its longitudinal axis, yet be configured to expand radially toprovide sufficient strength and stability to maintain the patency of thebody lumen. Since many commercial stents lack both the low profile andextreme flexibility needed to reach such distal lesions, they are notavailable for utilization for such procedures.

[0011] What has been needed is a stent which has a low profile and ahigh degree of flexibility so that it can be advanced through tortuouspassage ways of the anatomy and can be expanded within the body vesselto maintain the patency of the vessel. Additionally, the expanded stentmust have adequate structural strength (hoop strength) to hold the bodylumen open once expanded. Such a stent should also have sufficientradiopaque properties to permit it to be sufficiently visualized onexternal monitoring equipment, such as a fluoroscope, to allow thephysician to place the stent in the exact target location. The presentinvention satisfies these and other needs.

SUMMARY OF INVENTION

[0012] The present invention is directed to stents having low profileswhich can be used in body vessels, such as the carotid arteries andother peripheral arteries, along with the coronary arteries. The stentsof the present invention are intended, but are not limited, to theeffective treatment of diseased vessels having diameters from about 3.0to 14.0 millimeters.

[0013] The stents of the present invention can be formed from superelastic nickel titanium alloys, or other shape memory materials, whichallow the stent to be self expandable. The expansion occurs when thestress of compression is removed. This allows the phase transformationfrom martensite to austenite to occur, and as a result the stentexpands. The stents of the present invention can be processed to behavesuperelastically at body temperature. Alternatively, the stent designsof the present invention could be used in conjunction with balloonexpandable stents made from stainless steel or other conventional stentmaterials.

[0014] In all embodiments, the stents of the present invention havesufficient longitudinal flexibility along their longitudinal axis tofacilitate delivery through tortuous body lumens, yet remain stable whenexpanded radially to maintain the patency of a body lumen, such as anartery or other vessel, when implanted therein. The present inventionparticularly relates to unique strut patterns which have a high degreeof longitudinal flexibility and conformability, while providingsufficient radial-expansibility and strength to hold open the bodylumens. The high radial strength possessed by the stents of the presentinvention allow them to be used in treating calcified lesions.

[0015] Generally, the greater the longitudinal flexibility of thestents, the easier and the more safely they can be delivered to theimplantation site, particularly where the implantation site is on acurved section of a body lumen, such as a coronary artery or peripheralblood vessel, and especially in saphenous veins and larger vessels. Thedesigns of the present invention have sufficient flexibility to conformto the patient's vasculature, thus preventing vessel straightening bythe stent. Moreover, the stents of the present invention are crushproof, making them particularly suitable for implantation in the carotidarteries.

[0016] Each of the different embodiments of stents of the presentinvention include a plurality of adjacent cylindrical elements (oftenreferred to as “rings”) which are generally expandable in the radialdirection and arranged in alignment along a longitudinal stent axis. Thecylindrical elements are formed in a variety of serpentine wave patternstransverse to the longitudinal axis and contain a plurality ofalternating peaks and valleys. At least one interconnecting member(often referred to as a “spine”) extends between adjacent cylindricalelements and connects them to one another. These interconnecting membersinsure minimal longitudinal contraction during radial expansion of thestent in the body vessel. The serpentine patterns have varying degreesof curvature in the regions of peaks and valleys and are adapted so thatradial expansion of the cylindrical elements are generally uniformaround their circumferences during expansion of the stent from thecollapsed position to the expanded position.

[0017] The stents of the present invention also have strut patternswhich enhance the strength of the ends of the stent and the overallradiopacity of the stent, yet retain high longitudinal flexibility alongtheir longitudinal axis to facilitate delivery through tortuous bodylumens and remain stable when expanded radially to maintain the patencyof the body lumen. The present invention in particular relates to stentswith unique end portions having sufficient hoop strength to maintain aconstant inner diameter which prevents the stent from taking on a“cigar” shape when deployed in the body lumen. The end rings used withthe present invention are particularly useful on self-expanding stentswhich may otherwise have end rings that are more susceptible tocompressive forces.

[0018] The resulting stent structures are a series of radiallyexpandable cylindrical elements that are spaced longitudinally closeenough so that small dissections in the wall of a body lumen may bepressed back into position against the luminal wall, but not so close asto compromise the longitudinal flexibility of the stent both whennegotiating through the body lumens in their unexpanded state and whenexpanded into position within the vessel. The design of the stentscontribute to form small gaps between struts to minimize tissueprolapse. Each of the individual cylindrical elements may rotateslightly relative to their adjacent cylindrical elements withoutsignificant deformation, cumulatively providing stents which areflexible along their length and about their longitudinal axis, but whichstill are very stable in their radial direction in order to resistcollapse after expansion.

[0019] In one embodiment of the present invention, each cylindricalelement of the stent includes eight peak regions (often referred to as“crowns”) and eight valley regions which provide sufficient coverage ofthe vessel when placed in the expanded or deployed position. In thisdesign, each cylindrical element consisting of an alternating pattern ofU-shaped portions and double-curved (W) portions connected both axiallyand circumferentially to eight discontinuous interconnecting members orspines. For example, the U-shaped portion of the cylindrical element canbe connected to an adjacent cylindrical element via the interconnectingmembers. The same cylindrical element can be then connected to anothercylindrical element via the interconnecting members connected to thedouble-curved portions. The cylindrical element can be connected to anadjacent cylindrical element by four interconnecting members. Thisparticular alignment of interconnecting members provides adequateflexibility to the stent and also helps prevent foreshortening of thestent as it expands radially outward. The discontinuing pattern ofinterconnecting members results in a highly flexible stent that does notkink upon bending. Both the distal and proximal ends of this stentdesign can be entirely composed of “W” patterns which provide additionalstrength to the ends of the stent. The resulting stent produces an eightcrown, four-cell pattern which has sufficient coverage for vesselscaffolding while maintaining excellent flexibility to reach distallesions and possessing sufficient radial strength to hold the targetvessel open. An alternative pattern using six crowns and sixdiscontinuous interconnecting members also can be utilized and willexhibit these same physical properties.

[0020] The serpentine pattern of the individual cylindrical elements canoptionally be in phase with each other in order to reduce thecontraction of the stent along their length when expanded. In theseembodiments of the present invention, interconnecting members alignbehind each other to create a continuous “spine” which extends from oneend of the stent to the other. Two or three rows of continuous spinescan be used to connect adjacent cylindrical elements. This constructionalso helps prevent the stent from foreshortening when expanded.

[0021] A stent made in accordance with the present invention can bereadily delivered to the desired target location by mounting it on astent delivery catheter which includes a retractable sheath, or othermeans, to hold the stent in its collapsed position prior to deployment.

[0022] These and other features and advantages of the present inventionwill become more apparent from the following detailed description of theinvention, when taken in conjunction with the accompanying exemplarydrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is an elevational view, partially in section, depicting thestent embodying features of the present invention mounted on a deliverycatheter disposed within a vessel.

[0024]FIG. 2 is an elevational view, partially in section, similar tothat shown in FIG. 1, wherein the stent is expanded within a vessel,pressing the lining against the vessel wall.

[0025]FIG. 3 is an elevational view, partially in section, showing theexpanded stent within the vessel after withdrawal of the deliverycatheter.

[0026]FIG. 4 is a plan view of one preferred embodiment of a flattenedstent of the present invention, which illustrates the serpentine patternincluding peaks and valleys which form the cylindrical elements of thestent and permit the stent to achieve a small crimp profile, yet isexpandable to a larger diameter to maintain the patency of a smallvessel.

[0027]FIG. 5 is an enlarged partial view of the stent of FIG. 4depicting the serpentine pattern along with the peaks and valleys whichform one preferred embodiment of a cylindrical element made inaccordance with the present invention.

[0028]FIG. 6 is a plan view of an alternative embodiment of a flattenedstent of the present invention, which illustrates the serpentine patternalong with the peaks and valleys which form the cylindrical elements ofthe stent and permit the stent to achieve a small crimp profile, yet isexpandable to a larger diameter to maintain the patency of a smallvessel.

[0029]FIG. 7 is an enlarged partial view of the stent of FIG. 6depicting the serpentine pattern along with the peaks and valleys whichform another preferred embodiment of a cylindrical element made inaccordance with the present invention.

[0030]FIG. 8 is a plan view of an alternative embodiment of a flattenedstent of the present invention, which illustrates the serpentine patternalong with the peaks and valleys which form the cylindrical elements ofthe stent and permit the stent to achieve a small crimp profile, yet isexpandable to a larger diameter to maintain the patency of a smallvessel.

[0031]FIG. 9 is an enlarged partial view of the stent of FIG. 8depicting the serpentine pattern along with the peaks and valleys whichform another preferred embodiment of a cylindrical element made inaccordance with the present invention.

[0032]FIG. 10 is a plan view of an alternative embodiment of a flattenedstent of the present invention, which illustrates the serpentine patternalong with the peaks and valleys which form the cylindrical elements ofthe stent and permit the stent to achieve a small crimp profile, yet isexpandable to a larger diameter to maintain the patency of a smallvessel.

[0033]FIG. 11 is an enlarged partial view of the stent of FIG. 10depicting the serpentine pattern along with the peaks and valleys whichform another preferred embodiment of a cylindrical element made inaccordance with the present invention.

[0034]FIG. 12 is an enlarged view of a double-curved portion (w) whichhas a sweep cut which helps the stent to be crimped to a low diameter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Prior art stent designs, such as the MultiLink Stent™manufactured by Advanced Cardiovascular Systems, Inc., Santa Clara,Calif., include a plurality of cylindrical rings that are connected bythree connecting members between adjacent cylindrical rings. Each of thecylindrical rings is formed of a repeating pattern of U-, Y-, andW-shaped members, typically having three repeating patterns forming eachcylindrical element or ring. A more detailed discussion of theconfiguration of the MultiLink Stent™ can be found in U.S. Pat. No.5,569,295 (Lam) and U.S. Pat. No. 5,514,154 (Lau et al.), whose contentsare hereby incorporated by reference.

[0036] Beyond those prior art stents, FIG. 1 illustrates an exemplaryembodiment of stent 10 incorporating features of the present invention,which stent is mounted onto delivery catheter 11. FIG. 4 is a plan viewof this exemplary embodiment stent 10 with the structure flattened outinto two dimensions to facilitate explanation. Stent 10 generallycomprises a plurality of radially expandable cylindrical elements 12disposed generally coaxially and interconnected by interconnectingmembers 13 disposed between adjacent cylindrical elements 12. Thedelivery catheter 11 has an inner tubular member 14 upon which thecollapsed stent 10 is mounted. A restraining sheath 15 extends over boththe inner tubular member 14 and stent 10 in a co-axial relationship. Thestent delivery catheter 11 is used to position the stent 10 within anartery 16 or other vessel. The artery 16, as shown in FIG. 1, has adissected or detached lining 17 which has occluded a portion of thearterial passageway.

[0037] In a preferred embodiment, the delivery of the stent 10 isaccomplished in the following manner. Stent 10 is first mounted onto thedelivery catheter 11 with the restraining sheath placed over thecollapsed stent. The catheter-stent assembly can be introduced withinthe patient's vasculature in a conventional Seldinger technique througha guiding catheter (not shown). A guide wire 18 is disposed through thedamaged arterial section with the detached or dissected lining 17. Thecatheter-stent assembly is then advanced over guide wire 18 withinartery 16 until the stent 10 is directly under the detached lining 17.The restraining sheath 15 is retracted exposing the stent 10 andallowing it to expand against the inside of artery 16, which isillustrated in FIG. 2. While not shown in the drawing, artery 16 ispreferably expanded slightly by the expansion of stent 10 to seat orotherwise embed stent 10 to prevent movement. Indeed, in somecircumstances during the treatment of stenotic portions of an artery,the artery may have to be expanded considerably in order to facilitatepassage of blood or other fluid there through.

[0038] While FIGS. 1-3 depict a vessel having detached lining 17, stent10 can be used for purposes other than repairing the lining. Those otherpurposes include, for example, supporting the vessel, reducing thelikelihood of restenosis, or assisting in the attachment of a vasculargraft (not shown) when repairing an aortic abdominal aneurysm.

[0039] In general, stent 10 serves to hold open the artery 16 aftercatheter 11 is withdrawn, as illustrated in FIG. 3. Due to the formationof stent 10, the undulating component of the cylindrical elements ofstent 10 is relatively flat in a transverse cross-section so that whenstent 10 is expanded, cylindrical elements 12 are pressed into the wallof artery 16 and as a result do not interfere with the blood flowthrough artery 16. Cylindrical elements 12 of stent 10 that are pressedinto the wall of artery 16 will eventually be covered with endothelialcell growth that further minimizes blood flow turbulence. The serpentinepattern of cylindrical sections 12 provide good tacking characteristicsto prevent stent movement within the artery. Furthermore, the closelyspaced cylindrical elements 12 at regular intervals provide uniformsupport for the wall of artery 16, and consequently are well adapted totack up and hold in place small flaps or dissections in the wall ofartery 16 as illustrated in FIGS. 2 and 3.

[0040] The stresses involved during expansion from a low profile to anexpanded profile are generally evenly distributed among the variouspeaks and valleys of stent 10. Referring now to FIGS. 4-5, one preferredembodiment of the present invention as depicted in FIGS. 1-3 is shownwherein each expanded cylindrical element 12 embodies a serpentinepattern having a plurality of peaks and valleys that aid in the evendistribution of expansion forces. In this exemplary embodiment,interconnecting members 13 serve to connect adjacent valleys of eachadjacent cylindrical element 12 as described above. The various peaksand valleys generally have U, W and inverted-U shapes, in a repeatingpattern to form each cylindrical element 12. It should be appreciatedthat the cylindrical element 12 can be formed in different shapeswithout departing from the spirit and scope of the present invention.

[0041] The cylindrical element 12 of this stent 10 includesdouble-curved portions (W) 21 located in the region of the valley whereeach interconnecting member 13 is connected to an adjacent cylindricalelement 12. The peak portions (inverted-U) 22 and the valley portions(U) 23 also form the cylindrical element 12 of the stent 10. A shoulderregion 24 extending from each valley portion to peak portion (invertedU) 22 allows the peak portion to be nested in a tight formation next toan adjacent cylindrical element 12. This shoulder region 24 provides atransition region between the peak portions (inverted U) 22 and thevalley portions (U) 23 and double-curved portion (W) 21 to allowadjacent cylindrical elements to nest within one another and therebybetter support the artery walls with smaller gaps between stent struts.In this manner, the shoulder region 24 provides more dense coverage ofthe serpentine pattern of the cylindrical element to create a fairlyuniform strut pattern which fully supports the walls of the diseasedartery. For this reason, there are no or few areas of the stent wallwhich do not have struts for supporting the wall of the artery. Each ofthe valley portions (U) 23 forms a Y-shaped member when connected to aninterconnecting member 13. As can be seen in this particular design,each of the valley portions (W's and U's) 21 and 23 have aninterconnecting member which connects that cylindrical element 12 to anadjacent cylindrical element. As a result, each cylindrical element 12is connected to an adjacent cylindrical element by at least fourinterconnecting members 13. The peak portions (inverted “U”) 22 are notdirectly connected to any adjacent cylindrical element to allow forradial expansion. The eight interconnecting members 13 which areconnected to each cylindrical element 12 are discontinuous with eachother to produce a highly flexible stent that does not kink uponbending. This particular design allows the stent 10 to be placed intortuous anatomy, where the stent 10 will conform to the particularanatomy of the patient. For example, if the stent 10 is placed in acurved portion of a artery, then the flexibility of the stent will allowit to take on the same curved shape without kinking and will still becapable of fully supporting the artery. Additionally, the stent'sresistence to kinking helps prevent occlusion of the vessel lumen by thestent struts. Even though the stent 10 is flexible, it is still rigidwhen collapsed so that it can be placed on the delivery catheter andmoved into the desired location in the patient's vasculature.

[0042] The stent 10 also includes end rings 25 and 26 which comprise all“W” shaped portions 27 to provide additional strength to the ends of thestent 10. This “W” pattern also helps to increase the overallradiopacity of the stent by virtue of the additional material needed tocreate such a “W” pattern. As a result, the stent 10 should be easilyobservable by a physician using imaging instrumentation, such as afluoroscope.

[0043] In another embodiment of the present invention, as is shown inFIGS. 6 and 7, the stent 10 made with six crowns or peak portions(inverted U) 22, rather than the eight crowns shown in the previousembodiment. Otherwise, the strut pattern is virtually identical. Thestent shown in FIGS. 6 and 7 include six valley portions, namely threevalley portions (W) 21 and three valley portions (U) 23. This particulardesign also has six discontinuous interconnecting members 13 whichconnect each cylindrical element 12 to an adjacent cylindrical element.Again, the interconnecting member 13 are connected to each of the valleyportions (W) 21 and valley portion (U) 23 to help prevent shortening ofthe stent during radio expansion. This pattern also helps increase theflexibility of the strut. End rings 25 and 26 which comprise of all “W”shaped portions 27 provide additional strength to the ends of the stent10, while increasing the radiopacity of the stent as well.

[0044] In another embodiment of the invention, as shown in FIGS. 8 and9, the stent 30 is made with cylindrical elements 32 which include sixcrowns or peak portions (inverted U's) 29 and six valley portions,namely three valley portions (W) 31 and three valley portions (U) 34.This particular design differs from the previous two embodiments byutilizing three continuous interconnecting members 33 which are utilizedto connect each of the cylindrical elements 32 to an adjacentcylindrical element. Each interconnecting member 33 is connected to thevalley portion (W) 31 which creates a continuous spine 35 which extendsfrom one end 36 to the other end 37 of the stent 30. In this manner, theserpentine pattern of each individual cylindrical element 30 are inphase with each other in order to help reduce the contraction of thestent along their lengths when expanded. These continuous spines 35 helpprevent the stent 30 from shortening when each of the cylindricalelements 30 are radially expanded.

[0045] The cylindrical element 32 also differs from the previousembodiments since a valley portion (U) 34 is not utilized tointerconnect adjacent cylindrical elements to each other. However, thecylindrical element 32 includes a shoulder region 38 which extendsbetween each of the valley portions and peak portions to provide atransition region which allows the peak portion (inverted U) 29 to becrimped in close proximity to an adjacent cylindrical element. In thismanner, the stent 30 can be crimped down to a low profile which helpsreduce the overall profile of the stent and delivery catheter whenplacing the stent 30 through the tortuous anatomy of the patient'svasculature.

[0046] In still another embodiment of the present invention, as is shownin FIGS. 10 and 11, a stent 40 is shown having a plurality ofcylindrical elements 42 which are connected together by interconnectingmembers 43. Each of the cylindrical elements 42 include a peak portion(inverted U) 39 and valley portions (W) 41 and valley portions (U) 44which form the composite ring. In this particular design, five valleyportions (W) 41 are utilized and each of the cylindrical element 42 isconnected to an adjacent cylindrical element 42 by an interconnectingmember 43 which is connected to the valley portion (W) 41. As with theprevious embodiment, each interconnecting member 43 extends directlybehind one another to form a continuous spine 45 which extends from oneend 46 to the other end 47 of the stent 40. In this particularembodiment, five continuous spines 45 are created on the composite stent40. The peak portions (inverted U) 39 and the valley portion (U) 44 arenot connected by any interconnecting members. The end ring 48 of thisparticular stent 40 includes five double curved portions (W) 41 whichhelps increase the radial strength of this end while enhancing theradiopacity as well. As can be seen from the single cylindrical element42 shown in FIG. 11, the double curved portion (W) 41 include a “sweepcut” 49 which helps to reduce the collapsed profile of the stent 40 whenit is placed on a delivery catheter. This reduced portion of the doublecurved portion (W) 21 enables the peak portion (inverted U) 39 to becollapsed closer to the double curved portion (W) 41 without hitting thedouble-curved portion (W) 41 when the stent 40 is crimped onto thedelivery catheter. As a result, there should be no metal to metalcontact when the stent is crimped and the stent 40 should be crimped onto an even smaller profile which again helps in reducing the overprofile of the stent and delivery catheter and in reaching tight distalvessels. While this sweep cut 49 is shown only in conjunction with theembodiment shown in FIGS. 10 and 11, this sweep cut could be created onany of the other embodiments disclosed herein to help and reduce theoverall diameter of the stents when they are being crimped on to thestent delivery catheters.

[0047] It should be appreciated that the present design can be made witha number of peaks and valleys ranging from 4 to 16. The number of peaksand valleys will depend upon the particular physical characteristicsdesired, along with the particular application to which the stent willbe used.

[0048] In many of the drawing figures, the present invention stent isdepicted flat, in a plan view for ease of illustration. All of theembodiments depicted herein are cylindrically-shaped stents that aregenerally formed from tubing by laser cutting as described below.

[0049] One important feature of all of the embodiments of the presentinvention is the capability of the stents to expand from a low-profilediameter to a larger diameter, while still maintaining structuralintegrity in the expanded state and remaining highly flexible. Stents ofthe present invention each have an overall expansion ratio of about 1.0up to about 5.0 times the original diameter, or more, using certaincompositions of materials. The stents still retain structural integrityin the expanded state and will serve to hold open the vessel in whichthey are implanted. Some materials may afford higher or lower expansionratios without sacrificing structural integrity.

[0050] While the stent design of the present invention has verypractical applications for procedures involving vessel diameters fromabout 3.0 to 14.0 millimeters, it should be appreciated that the stentpattern could also be successfully used in procedures involving largerlumens of the body, without departure from the spirit and scope of thepresent invention. Due to the increase of the longitudinal flexibilityprovided by the present stent design, such applications could includelarger diameter vessels where added flexibility in reaching the vesselis needed.

[0051] The stents of the present invention can be made in many ways.However, the preferred method of making the stent is to cut athin-walled tubular member, such as Nitinol tubing to remove portions ofthe tubing in the desired pattern for the stent, leaving relativelyuntouched the portions of the metallic tubing which are to form thestent. It is preferred to cut the tubing in the desired pattern by meansof a machine-controlled laser.

[0052] A suitable composition of Nitinol used in the manufacture of aself expanding stent of the present invention is approximately 55%nickel and 44.5% titanium (by weight) with trace amounts of otherelements making up about 0.5% of the composition. The austenitetransformation temperature is between about −15° C. and 30° C. in orderto achieve superelasticity. The austenite temperature is measured by thebend and free recovery tangent method. The upper plateau strength isabout a minimum of 60,000 psi with an ultimate tensile strength of aminimum of about 155,000 psi. The permanent set (after applying 8%strain and unloading), is approximately 0.5%. The breaking elongation isa minimum of 10%. It should be appreciated that other compositions ofNitinol can be utilized, as can other self-expanding alloys, to obtainthe same features of a self-expanding stent made in accordance with thepresent invention.

[0053] The stent of the present invention can be laser cut from a tubeof super-elastic (sometimes called pseudo-elastic) nickel titanium(Nitinol) whose transformation temperature is below body temperature.All of the stent diameters can be cut with the same stent pattern, andthe stent is expanded and heat treated to be stable at the desired finaldiameter. The heat treatment also controls the transformationtemperature of the Nitinol such that the stent is super elastic at bodytemperature. The transformation temperature is at or below bodytemperature so that the stent will be superelastic at body temperature.The stent can be electro polished to obtain a smooth finish with a thinlayer of titanium oxide placed on the surface. The stent is usuallyimplanted into the target vessel which is smaller than the stentdiameter so that the stent applies a force to the vessel wall to keep itopen.

[0054] The stent tubing of a self expanding stent made in accordancewith the present invention may be made of suitable biocompatiblematerial besides super-elastic nickel-titanium (NiTi) alloys. In thiscase the stent would be formed full size but deformed (e.g. compressed)to a smaller diameter onto the balloon of the delivery catheter tofacilitate intra luminal delivery to a desired intra luminal site. Thestress induced by the deformation transforms the stent from an austenitephase to a martensite phase, and upon release of the force when thestent reaches the desired intra luminal location, allows the stent toexpand due to the transformation back to the more stable austenitephase. Further details of how NiTi super-elastic alloys operate can befound in U.S. Pat. Nos. 4,665,906 (Jervis) and 5,067,957 (Jervis).

[0055] The tubing also may be made of suitable biocompatible materialsuch as stainless steel. The stainless steel tube may be alloy-type:316L SS, Special Chemistry per ASTM F138-92 or ASTM F139-92 grade 2.

[0056] The stent diameters are very small, so the tubing from which itis made must necessarily also have a small diameter. For PTCAapplications, typically the stent has an outer diameter on the order ofabout 1 mm (0.04-0.09 inches) in the unexpanded condition, the sameouter diameter of the hypotubing from which it is made, and can beexpanded to an outer diameter of 4.0 mm or more. The wall thickness ofthe tubing is about 0.076-0.381 mm (0.003-0.015 inches). For stentsimplanted in other body lumens, such as PTA applications, the dimensionsof the tubing are correspondingly larger. While it is preferred that thestents be made from laser cut tubing, those skilled in the art willrealize that the stent can be laser cut from a flat sheet and thenrolled up in a cylindrical configuration with the longitudinal edgeswelded to form a cylindrical member.

[0057] Referring now to FIG. 5, the width of the strut of thecylindrical element, indicated by arrows 50, can be about from 0.003 to0.009 inches. The width of the strut of the interconnecting member,indicated by arrows 51, can be from about 0.003 to 0.009 inches. Thelength from the double-curved portion to the shoulder region, indicatedby arrow 52, can be from about 0.05 to 0.10 inches. The length from theshoulder region to the top of the peak portion, indicated by arrow 53,can be from about 0.05 to 0.10 inches. The width of the peak portions(unexpanded) indicated by arrows 54, can be from about 0.012 to 0.040inches. These same dimensions would apply specifically to theembodiments of the present invention shown in FIGS. 6 and 7 and theembodiment of FIGS. 8 and 9.

[0058] Referring now to FIG. 12 the width of the strut of thecylindrical element, indicated by arrows 50, can be about from 0.003 to0.009 inches. The width of the strut of the interconnecting member,indicated by arrows 51, can be from about 0.003 to 0.009 inches. Thelength from the double-curved portion to the peak portion, indicated byarrow 52, can be from about 0.070 to 0.150 inches. The width of the peakportions indicated by arrow 54, can be from about 0.03 to 0.06 inches.

[0059] Due to the thin wall and the small geometry of the stent pattern,it is necessary to have very precise control of the laser, its powerlevel, the focus spot size, and the precise positioning of the lasercutting path. In cutting the strut widths of the embodiment shown inFIGS. 1-5, it is preferable to have a very focused laser spot size whichwill allow the precise strut pattern to be created on the tubing. Forthis reason, additional instrumentation which includes a series oflenses may be necessary to be utilized with the laser in order to createthe fine focused laser spot necessary to cut that particular pattern.

[0060] Generally, the tubing is put in a rotatable collet fixture of amachine-controlled apparatus for positioning the tubing relative to alaser. According to machine-encoded instructions, the tubing is thenrotated and moved longitudinally relative to the laser which is alsomachine-controlled. The laser selectively removes the material from thetubing by ablation and a pattern is cut into the tube. The tube istherefore cut into the discrete pattern of the finished stent. Furtherdetails on how the tubing can be cut by a laser are found in U.S. Pat.Nos. 5,759,192 (Saunders) and 5,780,807 (Saunders), which have beenassigned to Advanced Cardiovascular Systems, Inc. and are incorporatedherein by reference in their entirety.

[0061] The process of cutting a pattern for the stent into the tubinggenerally is automated except for loading and unloading the length oftubing. For example, a pattern can be cut in tubing using a CNC-opposingcollet fixture for axial rotation of the length of tubing, inconjunction with CNC X/Y table to move the length of tubing axiallyrelative to a machine-controlled laser as described. The entire spacebetween collets can be patterned using the CO₂ or Nd:YAG laser set-up.The program for control of the apparatus is dependent on the particularconfiguration used and the pattern to be ablated in the coding.

[0062] After the stent has been cut by the laser, electrical chemicalpolishing, using various techniques known in the art, should be employedin order to create the desired final polished finish for the stent. Theelectropolishing will also be able to take off protruding edges andrough surfaces which were created during the laser cutting procedure.

[0063] While the invention has been illustrated and described herein interms of its use as intra vascular stents, it will be apparent to thoseskilled in the art that the stents can be used in other instances in allconduits in the body, such as, but not limited to, the urethra andesophagus. Other modifications and improvements may be made withoutdeparting from the scope of the invention.

What is claimed:
 1. A longitudinally flexible stent for implanting in asmall body lumen and expandable from a contracted condition to anexpanded condition, comprising: a plurality of adjacent cylindricalelements, each cylindrical element having a circumference extendingabout a longitudinal stent axis and being substantially independentlyexpandable in the radial direction, wherein the plurality of adjacentcylindrical elements are arranged in alignment along the longitudinalstent axis and form a generally serpentine wave pattern transverse tothe longitudinal axis containing a plurality of alternating valleyportions and peak portions, the valley portions including alternatingdouble curved portions and U-shaped portions; and a plurality ofinterconnecting members extending between the adjacent cylindricalelements and connecting the adjacent cylindrical elements to oneanother, interconnecting members being connected to the U-shapedportions to connect a cylindrical element to an adjacent cylindricalelement and interconnecting members being connected to the double-curvedportions to connect the cylindrical element to an adjacent cylindricalelement.
 2. The stent of claim 1, further including shoulder regionsinterconnecting the valley portions and peak portions.
 3. The stent ofclaim 1, wherein the double-curved portions have a reduced profile toallow the shoulder regions to collapse closer to each double-curvedportion.
 4. The stent of claim 2, wherein each cylindrical elementincludes approximately 4-16 alternating peak portions and valleyportions.
 5. The stent of claim 4, wherein interconnecting members areattached to each of the double-curved portions and U-shaped portions. 6.The stent of claim 5, further including shoulder regions interconnectingthe valley portions and peak portions.
 7. The stent of claim 6, whereinthe shoulder regions provide a transition region between the valleyportion and peak portions which allow the peak portions to have anarrower width.
 8. The stent of claim 1, wherein the stent is formedfrom a flat piece of material.
 9. The stent of claim 1, wherein thestent is formed from a piece of tubing.
 10. The stent of claim 1,wherein the stent is formed from a biocompatible material selected fromthe group consisting of stainless steel, tungsten, tantalum,superelastic nickel titanium alloys, and thermal plastic polymers. 11.The stent of claim 1, wherein each cylindrical element includes eightalternating peak portions and eight valley portions.
 12. The stent ofclaim 11, wherein the eight valley portions comprise of fourdouble-curved portions and four U-shaped portions.
 13. The stent ofclaim 1, wherein each cylindrical element includes six alternating peakportions and six valley portions.
 14. The stent of claim 13, wherein thesix valley portions comprise of three double-curved portions and threeU-shaped portions.
 15. The stent of claim 14, wherein interconnectingmembers are attached to each of the double-curved portions and U-shapedportions.
 16. The stent of claim 15, further including shoulder regionsinterconnecting the valley portions and peak portions.
 17. The stent ofclaim 1, further including cylindrical elements located at the ends ofthe stent which have a pattern of double-curved portions.
 18. The stentof claim 5, further including cylindrical elements located at the endsof the stent which have a pattern of double-curved portions.
 19. Thestent of claim 14, further including cylindrical elements located at theends of the stent which have a pattern of double-curved portions.
 20. Alongitudinally flexible stent for implanting in a small body lumen andexpandable from a contracted condition to an expanded condition,comprising: a plurality of adjacent cylindrical elements, eachcylindrical element having a circumference extending about alongitudinal stent axis and being substantially independently expandablein the radial direction, wherein the plurality of adjacent cylindricalelements are arranged in alignment along the longitudinal stent axis andform a generally serpentine wave pattern transverse to the longitudinalaxis containing a plurality of alternating valley portions and peakportions, the valley portions including alternating double curvedportions and U-shaped portions; and a plurality of interconnectingmembers extending between the adjacent cylindrical elements andconnecting the adjacent cylindrical elements to one another,interconnecting members being connected to the double-curved portion toconnect the cylindrical element to each adjacent cylindrical element.21. The stent of claim 20, further including shoulder regionsinterconnecting the valley portions and peak portions.
 22. The stent ofclaim 21, wherein the double-curved portions have a reduced profile toallow the peak regions to collapse closer to each double-curved portion.23. The stent of claim 20, wherein each of the cylindrical elements arein phase with each other and the interconnecting members attached to thedouble-curved portions align up in a continuous row which extends fromone end of the stent to the other.
 24. The stent of claim 23, whereineach cylindrical element includes six alternating peak portions and sixvalley portions.
 25. The stent of claim 24, wherein the six valleyportions comprise of three double-curved portions and three U-shapedportions.
 26. The stent of claim 25, wherein interconnecting members areattached to each of the double-curved portions.
 27. The stent of claim26, further including shoulder regions interconnecting the valleyportions and peak portions.
 28. The stent of claim 20, further includingcylindrical elements located at the ends of the stent which have apattern of double-curved portions.
 29. The stent of claim 27, furtherincluding cylindrical elements located at the ends of the stent whichhave a pattern of double-curved portions.
 30. The stent of claim 23,wherein each cylindrical element includes ten alternating peak portionsand ten valley portions.
 31. The stent of claim 30, wherein the tenvalley portions comprise of five double-curved portions and fiveU-shaped portions.
 32. The stent of claim 31, wherein interconnectingmembers are attached to each of the double-curved portions.